Field of the Invention
The present invention relates to a method for forming an image and a protective layer, and an apparatus therefor.
Background Art
Conventionally, a method is known in which image formation is performed using a thermal transfer sheet including color material layers which contain color materials, such as dyes, and by transferring the color materials onto an image receiving sheet. In such an image forming method, the formation of an image is carried out by: layering the thermal transfer sheet, and the image receiving sheet, which is a transfer receiving material; applying thermal energy provided by a heat source referred to as a thermal head to the thermal transfer sheet; and transferring the color materials of the thermal transfer sheet onto the image receiving sheet, which is the transfer receiving material. The image formation carried out by such a thermal transfer method allows for a gray scale adjustment by controlling the amount of energy applied from the thermal head to the thermal transfer sheet on a dot-by-dot basis, and is capable of forming of a high quality image comparable to a full-color photograph, which is extremely vivid as well as excellent in transparency, and color reproducibility and gradation of halftone.
A portion of the thermal energy provided for carrying out the thermal transfer is also applied to the surface of the transfer receiving material (image receiving sheet) through the thermal transfer sheet. The thermal head, which is the heat source for carrying out the thermal transfer, usually has a structure in which a plurality of heat generating elements is arranged in parallel with each other in a main scanning direction, on a pixel-by-pixel basis. When the thermal energy from the thermal head is applied to the thermal transfer sheet, the entirety of the thermal head does not function as an evenly heated heat source, and the temperature difference occurs between the portions of the thermal head at which the heat generating elements are provided (heat generating portions), and the portions thereof between the respective heat generating elements (non-heat generating portions). As a result, the thermal energy transferred to the surface of the transfer receiving material through the thermal transfer sheet will be unevenly distributed, corresponding to the temperature difference between the heat generating portions and the non-heat generating portions of the thermal head. This causes the occurrence of irregularities on the surface of the image receiving sheet, which is the transfer receiving material, thereby decreasing the smoothness and glossiness of the resulting image surface.
In view of the above mentioned problems, JP 6-336043 A (Patent Document 1) discloses an image forming method in which, after transferring color materials onto the surface of a transfer receiving material by thermal transfer, a line heater including a heat generating portion(s) extending continuously therein is used to transfer a transferable protective layer of a thermal transfer sheet onto the transfer receiving material, to form a protective layer thereon, so that the smoothness and glossiness of the resulting image can be improved. However, in the above described image forming method, it is necessary to prepare a thermal transfer printer which comprises a thermal head for forming an image, and the line heater for transferring the transferable protective layer. Therefore, there is a risk of an increase in the size of the printer and an increase in the production cost.
Further, JP 2005-125747 A (Patent Document 2) discloses an image forming method which utilizes a printer in which a pressing surface is provided on the surface of a thermal head, at a portion downstream in a transport direction of a transfer receiving material onto which an image has been formed. In this method, after transferring a transferable protective layer to form a protective layer on the image, the projected portions of the surface of the protective layer are pressed to flatten by the pressing surface of the thermal head, so that the smoothness and the glossiness of the surface of the protective layer can be improved.